1. Technical Field
The present invention relates to a transparent type liquid crystal display and more particularly to a transparent type liquid crystal display which can be suitably used as the display for information processing terminal equipment such as a word processor and a personal computer or the display for a color television.
2. Prior Art
Demands for a laptop computer, a notebook type computer or a small-sized color television have been rapidly increasing because of the recent space saving and increase in personal use. A display for use in these requires characteristics such as thinness, light weight and low-voltage driving. Therefore, a liquid crystal display (sometimes referred to as LCD for short, hereinafter) is most widely used at present.
Although a driving system using a super twisted nematic (hereinafter referred to as a STN) liquid crystal has been heretofore employed for LCD, an active matrix system using a thin film transistor (hereinafter referred to as a TFT) device or the like is now employed because LCD having a high image quality, a high density and a large capacity is obtained. A mode of display using a sheet polarizer such as a Twisted Nematic (hereinafter referred to as a TN) and an In Plane Switching (hereinafeter referred to as an IPS) is the mainstream of LCD using the TFT device. However, the mode using the sheet polarizer can easily achieve a high contrast in general, while this mode has a problem that transmittance is reduced because the sheet polarizer is used.
Means for solving such a problem may be that the sheet polarizer is replaced by an absorption mode such as a Guest-Host (hereinafter referred to as a GH) and a Polymer Dispersed Liquid Crystal (hereinafter referred to as a PDLC) in which liquid crystal is doped with dyes so that the transmittance is improved. Conversely, LCD with the high contrast cannot be, however, obtained because a dichromatic ratio or the like of the dyes for use in the absorption mode is low.
Moreover, the transmittance is limited by an area of a pixel which a light from a back light passes through, i.e., a so-called open area ratio, and the transmittance is determined in rough proportion to this open area ratio. Hence, another problem exists. That is, when the TFT device is increased in size or when a gate, a signal wiring or the like is broadly designed, the open area ratio is reduced and thus the transmittance is reduced.
An object of the present invention is to provide a novel transparent type liquid crystal display having the high contrast and the transmittance that does not depend on the open area ratio.